1. Field of Invention
The present invention relates to a variable compression ratio device, and more particularly, to a variable compression ratio device that changes a compression ratio by changing a volume of a combustion chamber.
2. Description of Related Art
In general, thermal efficiency of a heat engine increases as a compression ratio becomes higher. Here, the compression ratio is a ratio of a volume when gas flowing into a cylinder is compressed by a piston, and is represented by ‘a cylinder volume/a combustion chamber volume at a top dead center of a piston’. That is, the compression ratio increases as the top dead center of the piston becomes higher.
In the case of a spark ignition engine, thermal efficiency may be increased by advancing ignition timing, but there may be a limit in advancing the ignition timing when considering abnormal combustion. Therefore, there is a need for a variable compression ratio (VCR) device for improving thermal efficiency of the heat engine.
The variable compression ratio device is a device that changes a compression ratio of a gaseous mixture depending on a driving state of the engine. The variable compression ratio device improves fuel efficiency by raising a compression ratio of a gaseous mixture at a low load driving state (low load condition) of the engine. At a high load driving state (high load condition) of the engine, the variable compression ratio device serves to prevent the occurrence of knocking and improve engine output by maximally supplying the gaseous mixture, and simultaneously lowering the compression ratio of the gaseous mixture.
In the variable compression ratio device, a manner of moving a cylinder block, a manner of changing a volume of the combustion chamber, a manner of changing the top dead center of the piston, and the like are applied.
However, numerous mechanical constituent elements are required in order to implement the variable compression ratio device in the related art, and thus the configuration of the variable compression ratio device may be complicated. In addition, in a case in which a motor or the like, which uses electricity as a power source, is used to drive the mechanical constituent elements, there is a problem in that fuel efficiency may deteriorate.
Furthermore, since power transmission of the motor requires relatively larger drive torque than other gear engagement, there is a limit in that a capacity of the motor becomes small. Therefore, an overall weight of the vehicle may be increased, and fuel efficiency may deteriorate.
Meanwhile, since connection relationships between the mechanical constituent elements are complicated, it is difficult to ensure quick responsiveness of the variable compression ratio device.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.